The Cubs and Cardinals swapped minor leaguers as part of the Rule 5 Draft Thursday.

After the big-league portion of the Rule 5 Draft finished, the Cubs then selected outfielder Michael O'Neill from the Cardinals in the minor-league portion of the draft. St. Louis responded by nabbing left-handed pitcher Michael Heesch.

Heesch is a Chicagoland kid (born in Crystal Lake, Ill., and attended Prairie Ridge High School) who played for the Kane County Cougars in 2013-14.

The 25-year-old southpaw was drafted in the eighth round in 2012, but has pitched just one game above A-ball. He spent 2015 with Advanced Class-A Myrtle Beach, going 8-2 with a 2.24 ERA, 1.259 WHIP and three saves in 64.1 innings.

O'Neill is 27 and a former 31st-round pick of the 2010 Draft. He doesn't provide much power (four homers in 549 minor-league games), but has a knack for getting on base with a career .311 average and .412 on-base percentage in six minor-league seasons.

He had just spiked a fastball in the dirt to Cubs backup catcher Victor Caratini as Tuesday morning's sim game was winding down.

A couple moments later, Darvish fluttered one of his patented eephus pitches way up and out to Caratini and again let an expletive slip out.

Darvish threw about 55 pitches in three "innings" worth of a simulated game (meaning he sat down and rested for a few moments in between each "inning") while facing Caratini and David Bote with a host of onlookers including a gaggle of Chicago media, Joe Maddon and his maroon Levi's and Van's kicks, Theo Epstein and a group of Cubs coaches.

"It was good," Epstein said minutes after Darvish wrapped it up. "He was competing well out there, spinning the ball really well. Maybe his best spin of the year. That was good to see.

"We'll see how he feels tomorrow, but seems like he's just about ready for the next step, which should be rehab games."

Nobody knows how many rehab outings Darvish may need at this point and there's still no timetable for when the Cubs will get him back in the rotation.

Epstein acknowledged that at this point in the season — with less than seven weeks left until playoffs begin — the Cubs have just one shot to make this work with Darvish. Any setback now is essentially the dagger in any hopes of a comeback.

You can get giddy about the spin rate all you want, but the real telling sign to the Cubs was Darvish's attitude. Instead of worrying about his arm or any lingering pain out there, he was getting pissed at himself for missing spots as he started to tire in the sim game.

It was a sign to both Epstein and Maddon that Darvish is getting back in the right head space to return to a big-league field in the middle of a tight pennant race.

"I think he wants it," Epstein said. "The guys that are around him every day feel like he's really eager to get out there and compete. Even in the sim game today, when Vic had a good swing on the fastball, he came back on the next one a little bit harder and was mixing all his pitches.

"He's going about his business like someone who's on a mission to come back and help this team."

Maddon concurred.

"Totally engaged, looked really good, was not holding back," the Cubs skipper said. "...We were all very impressed."

All that being said, the Cubs still aren't in a place where they feel confident enough to just plug Darvish back into the rotation for the final few weeks of September and into October (assuming they make it there).

Darvish has said himself he feels like he turned a corner a couple weeks ago and is back in a good place physically.

Still, his journey back has already experienced several hiccups and there's no telling everything will be perfect from here.

At the end of the day, Maddon and his staff have no choice but to try to win ballgames with the guys who are on their active roster and can't worry about what "might be" with Darvish, Kris Bryant, Brandon Morrow or even Drew Smyly.

Of course, getting those guys back healthy would be a heck of a boon to this Cubs team, but it's not something they can count on.

"I don't think you ever get to that point," Epstein said. "... Anytime a player's injured, there's a certain probability that he returns and on a certain timetable and there's a spectrum of outcomes when he comes back. From being significantly better than he was before he went down to performing the same to not being effective.

"None of us can predict exactly what the outcome is gonna be, so you have to be prepared for all the possible outcomes. You never want the performance of any one player to be the linchpin of the success of the club. Because if you are, you're being irresponsible and setting yourself up to fail.

"At the same time, you're never gonna be as good as you might be if one of your most talented players returns and returns in really good form. We're hopeful and we're trying to do everything we can to put him in a position to succeed and right now, there've been a lot of good signs, which is certainly better than where we were six weeks ago."

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At a time when the Cubs are missing their closer and continuing to hold their lead on the division anyway, the Brewers are in a very different place.

Coming in to a short but weighty series at Wrigley Field, Milwaukee has dropped two games via bullpen meltdown in their last four. Corey Knebel, who saved 39 games for the Brewers in 2017 with a 1.93 ERA, has seen much more limited time in the closer's role this year. But getting him right will probably make the difference for Milwaukee down the stretch.

"It’s important that we get him going," Brewers manager Craig Counsell told reporters before Tuesday's game. "Getting Corey on track is probably the bigger equation in this that kind of normalizes the bullpen."

Last Thursday, Knebel loaded the bases in the 9th when Milwaukee was leading, 4-2, and eventually left for Joakim Soria after allowing a run on a single. This set the stage for Hunter Renfroe's grand slam that cost the Brewers the game. In his next appearance, Knebel pitched in the 5th inning against the Braves and gave up a run in Milwaukee's eventual 8-7 loss.

Without a reliable Knebel, the Brewers have had to play mix and match with their bullpen, a recipe that doesn't usually work. It's been successful so far for the Cubs in the absence of Morrow, but that hasn't been the case for Milwaukee lately.

The Brewers acquired Joakim Soria from the White Sox on July 26 in hopes of shoring up their bullpen, but after giving up the grand slam to Renfroe last week, Soria hit the DL with a right quadriceps strain. Counsell said that it isn't likely for Soria to return very soon, however.

"We’re not going to be at 10 days, I’ll tell you that," Counsell said, adding that Soria is still only doing stationary bike work at this point.

But help might be on the way. Taylor Williams, who was placed on the 10-day disabled list on August 3, is eligible to return. For now, the Brewers opted to keep outfielder Keon Broxton on the roster, but Williams could prove to be a boon for the Milwaukee reliever corps. Before being shelved, he was averaging more than a strikeout per inning.

Otherwise, the Brewers have Matt Albers rehabbing in Biloxi, Mississippi, where they plan to let him appear in at least a couple games before activating him.

Milwaukee has a chance to cut the division lead to a single game these next two days, but without a reliable bullpen, that could prove especially difficult.